Lab-meeting: between-sex covariance for dummies explained by Tom Gosden

Posted by Erik Svensson

Next week, EXEB-member Tom Gosden will give a practice talk of his forthcoming Friday seminar about between-sex covariance and genetic constraints on the evolution of sexual dimorphism.

As many of you already know, Tom is a former PhD-student in our laboratory, and is currently visiting postdoc, until he will return to Brisbane in Australia where he will commence a Junior Research position.

Tom's informal talk will be about fruitflies (Drosophila) and how to understand, interpret and estimate between-sex genetic covariance, and Tom has promised to explain it also to non-experts. Note that the lab-meeting time has been changed to afternoon from morning and to another locality on 3rd floor. For those of you who want to get a deeper idéa what Tom's research is about, here is a link to a recent article he published in Evolution.

When: Tuesday March 4 2014, 14.00-15.30
Where: Seminar room "Communis", 3rd floor (Ecology Building)

 Everybody should be most welcome!

THE B-MATRIX HARBORS SIGNIFICANT AND SEX-SPECIFIC CONSTRAINTS ON THE EVOLUTION OF MULTICHARACTER SEXUAL DIMORPHISM 

Thomas P. Gosden, Krishna-Lila Shastri, Paolo Innocenti, Stephen F. Chenoweth

The extent to which sexual dimorphism can evolve within a population depends on an interaction between sexually divergent selection and constraints imposed by a genetic architecture that is shared between males and females. The degree of constraint within a population is normally inferred from the intersexual genetic correlation, rmf. However, such bivariate correlations ignore the potential constraining effect of genetic covariances between other sexually coexpressed traits. Using the fruit fly Drosophila serrata, a species that exhibits mutual mate preference for blends of homologous contact pheromones, we tested the impact of between-sex between-trait genetic covariances using an extended version of the genetic variance–covariance matrix, G, that includes Lande's (1980) between-sex covariance matrix, B. We find that including B greatly reduces the degree to which male and female traits are predicted to diverge in the face of divergent phenotypic selection. However, the degree to which B alters the response to selection differs between the sexes. The overall rate of male trait evolution is predicted to decline, but its direction remains relatively unchanged, whereas the opposite is found for females. We emphasize the importance of considering the B-matrix in microevolutionary studies of constraint on the evolution of sexual dimorphism.

Lab-meeting on March 16 2011. New paper on condition-dependent sexual signalling by exiled lab-member Tom Gosden

Next week's lab-meeting we will not read any paper, but instead Machteld Verzijden and myself will give some informal presentations of the talks we will give in a small symposium on insect behaviour and evolution in Stockholm on Thursday, that is arranged by Professor Christer Wiklund in conjunction with a PhD-defence by his student Martin Bergman. Both Machteld and I will of course be happy for any feedback you might have, the day before our official presentations. The title of Machtelds talk is "Ethological speciation mechanisms" and mine is "Ecological vs. non-ecological speciation mechanisms".

If you nevertheless have time and are interested in reading a cool paper, there is one good one that has just been published in Journal of Evolutionary Biology by Tom Gosden and Steve Chenoweth. As you know, Tom is currently in exile in Australia, funded by a Marie Curie "outgoing" postdoc, where he now studies the fascinating and charismatic fruitfly Drosophila serrata, which has recently emerged as somewhat of a model organism in evolutionary quantitative genetics and sexual selection studies. Steve Chenoweth and Mark Blows are leading researchers in this field and have developed sophisticated statistical techniques to estimate breeding values and selection on such breeding values in this species.

The present study tests assumptions behind so-called "genic capture"-model of sexual selection, by looking at the degree of condition-dependence and genetic variation for in condition-dependence among males of Drosophila serrata in relation to a novel food source (yeast). Interestingly, the authors found evidence for condition-dependent sexual signalling, but apparently no genetic variation for condition-dependence, which indicates that it cannot evolve further, at least on this food source. Beware of some heavy maths and statistitics, before you decide to read this paper! Tom will return to Lund in 2012 (same year as Yuma) and bring in fresh new knowledge and skills to our group that he learned in Australia. Below is the abstract of their fascinating paper:

On the evolution of heightened condition dependence of male sexual displays

T. P. GOSDEN & S. F. CHENOWETH

The maintenance of genetic variation in male sexual display traits in the face of strong directional sexual selection from female preferences is an ongoing evolutionary conundrum. Condition dependence and the genic capture hypothesis are often cited as theoretical resolutions to this problem, yet little is known about the ability of condition dependence itself to evolve. We set out to test how a suite of cuticular hydrocarbons (CHCs) used in sexual displays are affected by adult diet and the potential for any condition-dependent response to evolve in a laboratory-adapted population of the Australian fruit fly Drosophila serrata. We performed a dietary manipulation within a half-sib breeding design, raising adult males either with or without access to live yeast, a manipulation that had previously shown strong effects on female fitness. Diet had strong phenotypic effects, with males from the different diets producing different CHC blends. The blend of CHCs under sexual selection showed a degree of elevated condition dependence. Regardless of the heightened sensitivity of favoured CHC blends to diet and the presence of genetic variance for the traits, we were unable to detect any genetic variance in the reaction norms for the male dietary response. Our results suggest that there is limited opportunity for males to evolve further condition dependence in response to yeast availability in this population.